Implement register class inflation.

When splitting a live range, the new registers have fewer uses and the
permissible register class may be less constrained. Recompute the register class
constraint from the uses of new registers created for a split. This may let them
be allocated from a larger set, possibly avoiding a spill.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110703 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SplitKit.cpp

@@ -571,6 +571,7 @@ void SplitEditor::rewrite() {
   VirtRegAuxInfo vrai(vrm_.getMachineFunction(), lis_, sa_.loops_);
   for (unsigned i = firstInterval, e = intervals_.size(); i != e; ++i) {
     LiveInterval &li = *intervals_[i];
+    vrai.CalculateRegClass(li.reg);
     vrai.CalculateWeightAndHint(li);
   }
 }